The correct answer is work ethic.
Improving performance and striving for a better career is an example of work ethic.
You have a work ethic when you are committed to doing what it takes in order to improve your actual situation. Work ethic means that you focus a hundred percent on the necessary things that will make you better, and you do it on a daily basis. No short cuts, no excuses. Your work ethic means that you will not rest until you get what you want, with discipline, perseverance, doing legal things, and showing respect to other people that are trying to do the same.